Application Of Active And Passive Source Surface Wave Methods In The Tunnel Exploration Of He Yan Road,Nanjing

With the rapid development of the national economy,the construction of roads,railroads and other basic transportation facilities has been rapidly promoted,involving more and more tunnel exploration work during construction.The exploration tasks related to tunnel engineering mainly involve the detection of stratigraphic lithology,geological structures,adverse geological bodies and groundwater.Due to the limitations of cost,time and site conditions,it is not possible to use a large number of drilling work to carry out the detection,only with the help of geophysical methods.In urban areas,there are constraints such as complex environment and serious human noise interference,which make it difficult for traditional geophysical methods(such as electromagnetic methods)to work to collect reliable data.The Rayleigh wave method,which has emerged in recent years,has the advantages of high data signal-to-noise ratio,strong antiinterference ability and high interpretation accuracy.So it is the preferred means for geological exploration of tunnel in complex urban environments.This paper takes the geological structure detection of the He Yan Road tunnel in Qixia District,Nanjing as the research objective.Firstly,based on the propagation law and dispersion theory of Rayleigh waves,a series of velocity models of different types of typical stratigraphic structures were established by combining the actual tunnel geophysical conditions.The corresponding Rayleigh wave dispersion curves were calculated by vector transfer algorithm,and the relationship and characteristics between velocity parameters and dispersion curves were summarized and analyzed.The imaging study was carried out by global optimization genetic algorithm,from forward simulation and inverse imaging,which provides a theoretical basis for the Rayleigh wave method for the geological exploration of river crossings.Then,using the phase shift method,spatial autocorrelation method,discuss the excellence of extracting Rayleigh wave dispersion energy curve from the active and passive source field data,the results show that: the active source surface wave method to obtain a high frequency Rayleigh wave signal,shallow resolution,the passive source surface wave method to extract the Rayleigh wave signal from various types of background noise,the use of low-frequency signals to detect the deep strata,the use of dualsource joint imaging technology makes the advantages complementary,improving the imaging accuracy and depth.Finally,using the theoretical and technical methods described above,combined with the active source and passive source surface wave data collected from the river crossing tunnel in Qixia District,Nanjing,the location of the bedrock surface in the work area was obtained,the stability conditions of the site were evaluated,and undesirable geological bodies such as karst cavities along the route were identified,and the imaging results matched the existing borehole data,providing valuable geological exploration information for the next tunnel excavation.